During manufacturing of a MEMS device, such as pressure sensors, acceleration sensors, microphones or loudspeakers, deep cavities may be formed. The deep cavities can be bulk micro-machined. One example of a deep cavity is a back cavity of some designs of a MEMS microphone. Moreover, in some manufacturing processes relative to MEMS devices, a sacrificial layer may have to be removed by sacrificial layer etching. Sacrificial layer etching may require that an etching agent has to be provided through etch holes within one or more layers that is/are adjacent to the sacrificial layer so that the etching agent can reach the sacrificial layer.
In operation, this cavity within, for example, a MEMS microphone can be used as a volume in which air is able to expand. In many cases, the openings of such cavities are relatively small compared to their respective depths. This case is called high aspect ratio.